TNF-α Induces Phenotypic Modulation in Cerebral Vascular Smooth Muscle Cells: Implications for Cerebral Aneurysm Pathology

• Published in: Journal of cerebral blood flow and metabolism 2013-10, Vol.33 (10), p.1564-1573
• Main Authors: Ali, Muhammad S, Starke, Robert M, Jabbour, Pascal M, Tjoumakaris, Stavropoula I, Gonzalez, L Fernando, Rosenwasser, Robert H, Owens, Gary K, Koch, Walter J, Greig, Nigel H, Dumont, Aaron S
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis - drug effects; Apoptosis - genetics; Carotid Arteries - drug effects; Carotid Arteries - pathology; Cell Differentiation - drug effects; Cell Differentiation - genetics; Cells, Cultured; Circle of Willis - drug effects; Circle of Willis - metabolism; Circle of Willis - pathology; Disease Models, Animal; Dose-Response Relationship, Drug; Epigenesis, Genetic; Genetic Markers - drug effects; Intracranial Aneurysm - genetics; Intracranial Aneurysm - immunology; Intracranial Aneurysm - pathology; Kruppel-Like Transcription Factors - genetics; Kruppel-Like Transcription Factors - physiology; Muscle, Smooth, Vascular - drug effects; Muscle, Smooth, Vascular - metabolism; Muscle, Smooth, Vascular - pathology; Nuclear Proteins - genetics; Original; Promoter Regions, Genetic; Rats; Thalidomide - analogs & derivatives; Thalidomide - pharmacology; Trans-Activators - genetics; Transcriptome; Tumor Necrosis Factor-alpha - antagonists & inhibitors; Tumor Necrosis Factor-alpha - pharmacology; Tumor Necrosis Factor-alpha - physiology
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1038/jcbfm.2013.109

Little is known about vascular smooth muscle cell (SMC) phenotypic modulation in the cerebral circulation or pathogenesis of intracranial aneurysms. Tumor necrosis factor-alpha (TNF-α) has been associated with aneurysms, but potential mechanisms are unclear. Cultured rat cerebral SMCs overexpressing myocardin induced expression of key SMC contractile genes (SM-α-actin, SM-22α, smooth muscle myosin heavy chain), while dominant-negative cells suppressed expression. Tumor necrosis factor-alpha treatment inhibited this contractile phenotype and induced pro-inflammatory/matrix-remodeling genes (monocyte chemoattractant protein-1, matrix metalloproteinase-3, matrix metalloproteinase-9, vascular cell adhesion molecule-1, interleukin-1 beta). Tumor necrosis factor-alpha increased expression of KLF4, a known regulator of SMC differentiation. Kruppel-like transcription factor 4 (KLF4) small interfering RNA abrogated TNF-α activation of inflammatory genes and suppression of contractile genes. These mechanisms were confirmed in vivo after exposure of rat carotid arteries to TNF-α and early on in a model of cerebral aneurysm formation. Treatment with the synthesized TNF-α inhibitor 3,6-dithiothalidomide reversed pathologic vessel wall alterations after induced hypertension and hemodynamic stress. Chromatin immunoprecipitation assays in vivo and in vitro demonstrated that TNF-α promotes epigenetic changes through KLF4-dependent alterations in promoter regions of myocardin, SMCs, and inflammatory genes. In conclusion, TNF-α induces phenotypic modulation of cerebral SMCs through myocardin and KLF4-regulated pathways. These results demonstrate a novel role for TNF-α in promoting a pro-inflammatory/matrix-remodeling phenotype, which has important implications for the mechanisms behind intracranial aneurysm formation.